Convertible top assemblies with one or more hydraulically driven components are generally known, e.g from EP 0 425 156. In a known simple design, the hydraulic actuating device comprises a single hydraulic actuator for moving the convertible top, but in many cases there are a plurality of components which are each driven by one or more associated hydraulic actuators, for example the convertible top (which may comprise either a foldable cover or one or more rigid cover parts), the tonneau cover, one or more latches and, in the case of convertible tops with a foldable cover, the bow for tensioning the fabric.
One of the functions which is often carried out hydraulically is the movement of the convertible top itself from the open position to the closed position and vice versa. The hydraulic pressure which is required in order to carry out these movements is relatively low throughout most of these movements. However, in the vicinity of the end positions of the convertible top, it is often necessary to supply a greater force, for example in order to compress a sealing strip between the convertible top and the header above the windscreen, or owing to the relatively unfavourable engagement of the convertible top actuators on the convertible top in the open position. It may also be desirable/necessary to supply a greater force at other moments during the movement. Furthermore, some actuators have only a small active piston surface, so that a relatively great hydraulic pressure is required in order for these actuators to be able to drive the associated component. For example, in a number of convertible top assemblies one or more latches are hydraulically actuated, and the actual hydraulic actuators associated with these latches are often extremely small, in particular owing to the limited fitting space, and therefore require a high hydraulic pressure in order to drive the latch.
A significant drawback of the known hydraulically actuated convertible top assemblies is that it takes an undesirably long time to open and close the convertible top, while the market demands convertible top assemblies which work increasingly quickly.